This invention relates to a hardening composition for civil engineering and construction works, more specifically, to a hardening composition which gives a hardened product having high compressive strength and high bending strength, and such hardened product, and a method for producing such hardened product.
There has hitherto been known an inorganic hardening composition which contains an alkali metal silicate as a requisite hardening component, often referred to as water glass, and a hardening agent therefor. For example, Japanese Laid-open Patent Application No. 57-198782 discloses a method for stabilizing soil using a mixture of (A) an aqueous solution of sodium silicate and (B) a mixed aqueous solution of sodium hydrogensulfate and potassium chloride; or an aqueous solution of a mixture of the mixed aqueous solution and (a) magnesium oxide and/or magnesium hydroxide, and/or (b) at least one member selected from the group consisting of sodium dihydrogenphosphate, potassium dihydrogenphosphate, disodium hydrogenphosphate, dipotassium hydrogenphosphate, aluminum sulfate, magnesium sulfate, magnesium chloride, and potassium alum, with an addition of ethylene carbonate and/or propylene carbonate to the solution (B). The solutions (A) and (B) are mixed and hardened in the soil for stabilization. Further, U.S. Pat. No. 4,363,665 to Barrier et al. discloses a moldable composition of matter comprising an admixture of (1) sand, (2) an alkali metal silicate, (3) a hardening agent comprising an alkylene carbonate, carboxylic acid ester, or mixtures thereof, and (4) a demolding agent including a mixture of alkaline earth metal oxide or carbonate and a hydrate alumina. U.S. Pat. No. 4,683,019 to Motoki discloses a self-hardening refractory composition for coating on a steel column or steel beam, comprising at least one water-soluble alkali silicate, a hardener for the water-soluble alkali silicate such as bivalent or higher valent metal salts of higher fatty acids, and at least one material selected from the group consisting of a material containing bound water and a material capable of absorbing heat when heated.
On the other hand, there has hitherto been proposed a hardening composition which does not contain water glass as a requisite hardening component. This hardening composition has a totally different composition from that of the inorganic hardening composition as mentioned above. For example, compositions are known containing as the hardening component an alkaline earth metal hydroxide or an alkaline earth metal oxide. However, a type and mixing amount of a hardening agent for these hardening components vary depending on the type of the alkaline earth metal hydroxide or the alkaline earth metal oxide. Therefore, there has hardly been obtained a hardened product hardened within a practical hardening time and having a sufficient strength comparable to or higher than that of a hardened product containing water glass as the hardening component. In this regard, there has been proposed in U.S. Pat. No. 5,036,029 to Johnson to use an organic binder such as a urea-formaldehyde resin in addition to the hardening agent such as water, thereby reinforcing the binding force between the hardening components. However, studies have not been made on selection of the hardening agent itself.